Field
The present invention relates to a micro-electro-mechanical device for detecting angular velocity and especially to a three axis gyroscope.
Description of Related Art
Micro-Electro-Mechanical Systems, also called in short as MEMS can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have a mechanical functionality.
MEMS structures can be applied to quickly and accurately detect very small changes in physical properties. For example, a microelectronic gyroscope can be applied to quickly and accurately detect very small angular displacements.
Motion has six degrees of freedom: translations in three orthogonal directions and rotation around three orthogonal axes. The latter can be measured by an angular rate sensor, also known as gyroscope. In MEMS gyroscopes, Coriolis Effect is used to measure angular rate. When a mass is moving in one direction called primary motion and rotational angular velocity is applied, the mass experiences a force in orthogonal direction as a result of the Coriolis force. Resulting physical displacement caused by the Coriolis force may be then read from, for example, a capacitive, piezoelectrical or piezoresistive sensing structure. The displacement due to the Coriolis Effect may also be called detection motion or sense mode. The primary motion may alternatively be called primary mode or drive mode.
In a MEMS gyroscope, mechanical oscillation is used as the primary motion. When an oscillating gyroscope is subjected to an angular motion orthogonal to the direction of the primary motion, an undulating Coriolis force results. This creates a secondary oscillation, also referred to as the detection motion, orthogonal to the primary motion and to the axis of the angular motion, and at the frequency of the primary oscillation. The amplitude of this coupled oscillation can be used as the measure of the angular rate, i.e. the absolute value of angular velocity.
WO2010/097275 presents an electromechanical microsensor having three drive elements for determining two or three components of the yaw rate vector of the substrate. Three drive elements are connected to one another for synchronizing the driving movements by means of a coupling device. A problem relating to the presented solution is that reaction forces of the rotating coupling device between the drive elements introduce components to the motion of the drive elements that deviate from the optimal mutually perpendicular direction of the driving motion.